Most fifth wheels are built to accommodate a 2″ diameter kingpin, but some heavy-duty semitrailer tractors, such as the HET (Heavy Equipment Transport) used by the U.S. military, carry fifth wheels capable of accommodating 3½″ kingpins. Occasionally, it could be of value to have both capabilities available on a single tractor. Some prior art semitrailers have kingpins that may be detached from the trailer so that a kingpin of a different diameter can be reattached. However, not all semitrailers are so equipped, and the ones that are so equipped require that the existing kingpin be removed with a tool and that the alternative kingpin be installed with the tool.